Sheet metal blade and manufacture



July 23, 1957 S- WILDER, JR

SHEET METAL BLADE AND MANUFACTURE Filed Nov. 1, 1951 IN V EN TOR.

i 5 zzafi ZZz/Zegj! MWVM ATTORNEYS United States Patent SHEET NIETAL BLADE AND MANUFACTURE Stuart Wilder, Jr., Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 1, 1951, Serial No. 254,264

1 Claim. (Cl. 29156.8)

This invention relates to blading of a type specially suited for use in elastic fluid dynamic machines such as gas turbine engines and the like and more particularly to an improved construction for and the manufacture of hollow sheet metal or tubular blades.

The invention is particularly adapted to the manufacture of hollow buckets or blades primarily intended for use in the stators of turbines and axial flow compressors of gas turbine aircraft engines. The utilization of hollow blading for these purposes is especially desirable and offers many advantages over blades with solid bodies, as hollow blades afford substantial savings in cost, weight, and materials are, altogether, better adapted to cooler operation.

Axial flow compressor and turbine blades are generally of complex form, having usually an airfoil or crescent cross-section with one convex and one concave face, and may be tapered throughout their length. Aerodynamic and thermodynamic considerations dictate that such blading elements be formed with a sharp thin trailing edge and, in some cases with a similarly formed leading edge as well.

Among the numerous methods heretofore suggested for forming hollow blades have been various forging, pressing, or drawing processes or combinations thereof. It has been found, however, that the blading elements formed in accordance with these methods, as practiced in the past, have not been entirely satisfactory in that excessive strains and stress concentrations are encountered in substantially all cases where the blade has been bent, creased, or folded. These stress concentrations, usually appearing at the internal fold or crease of the material, inherently weaken the blade or bucket element and ultimately lead to cracking and splitting and consequent destruction thereof.

Accordingly, it is the general object of the present invention to provide an improved construction of and process for the manufacture of folded sheet metal or tubular blades, or other folded metal articles, wherein stress concentrations that previously have been encountered at the creased edge or edges thereof are substantially eliminated or mitigated. Other objects are to provide an improved form of hollow compressor blade or turbine bucket which is not only durable and light in weight, but which is of suflicient structural strength, and also simple and inexpensive to manufacture.

In accordance with the invention the stress concentration at the edge of a sharply folded hollow sheet metal blade is appreciably reduced by the inclusion of pre-positioned reinforcing means such as a length of wire within the internal crease of the material during the forming process and by subsequently forging, compressing, distorting or otherwise deforming the creased edge of the blade over the reinforcing means so as to embed the latter within the internal fold of the blade material, the material at the said internal gold of the blade being displaced by the wire.

The above and other objects, features and advantages of the present invention will appear more fully from the detailed description and drawings of the preferred embodiment of the invention, wherein:

Fig. 1 illustrates the step of positioning the original pieces from which the blade is formed prior to the first forming operation;

Figs. 2 and 3 illustrate the first and second forming operations;

Figs. 4 through 7, inclusive, illustrate the succession of subsequent operations for shaping the trailing edge of the blade;

Fig. 8 illustrates the final shaping operation;

Fig. 9 is a view along one of the blade faces of a hollow blade constructed in accordance with the present in vention, and

Fig. 10 is a cross-section taken on the plane 10-10 of the blade of Fig. 9.

By way of introduction, it may be advisable to refer first to Fig. 9 which illustrates a stator blade or vane which has been constructed in accordance with the process of the invention. The body of the blade 15 is hollow, and as shown in Fig. l, is of an air foil form in cross-section with one convex side or face 17 and one concave side or face 18, with a rounded leading edge 20 and a sharp, thin trailing edge 22. The blade is shown mounted between outer and inner shroud bands 24 and 26 of a compressor or turbine and is rigidly secured therebetween as by welding, for example.

In accordance with the invention, the strength of the blade is materially increased by the inclusion of reinforcing means such, for example, as a length of wire 28 which extends the length of the blade and is embedded within the inner crease of the material in the inner folded trailing edge 22 of the blade body.

Turning now to the preferred embodiment of the process of the invention, the body of the blade may be formed from a single flat metal blank 30 of appropriate shape and a strip of wire 28 extending across the surface of the blank at approximately the center thereof as illustrated in Fig. 1. The blade faces are formed from the portions 32, 34 of the blank on the opposite sides of the wire 28. The blank 39 may be prepared in any of a number of ways known to those skilled in the art, as by blanking or trimming, for example, from a strip or block of metal to the desired thickness of the blank. For greater blade strength the grain flow of the metal should preferably ze parallel to the length of the blank. The blank may be tapered in thickness toward the free end of the blade if desired.

The wire 28 may be round or otherwise suitably shaped and should preferably be in a fairly hard and non-malleable condition, and the blank preferably relatively soft, malleable or ductile so as to allow the material at the inner crease of the folded edge thereof to flow or be deformed about the wire during the subsequent shaping operations without deformation of the cross-section of the wire, as shown and described hereinafter. The wire 23 may be brazed to the surface of the blank to facilitate the subsequent operations, if desired.

Fig. 2 illustrates the initial forming of the trailing edge of the blade which involves folding back the portions 32, 34 of the blank 30 about the wire 28. This operation may be accomplished in various ways as by die forming the blank about the wire in a hydraulic press between suitably shaped folding dies such, for example, as the male die 36 and female die 38 shown. The male or punch portion 36 has a Wedge-shaped lowered portion and a grooved edge 40 that bears against the surface of the wire 28 and is caused, by the application of pressure thereto, to force both the wire and the flat blank V 3 into a groove 42. having a rounded bottom in the female die 38.

Fig. 3 illustrates the position of the wire and the blank for the second forming operation that may be performed in a hydraulic press, for example, employing a die set to force the sheet metal more completely around the wire 28. This 'die set may comprise a grooved die'43'to receive the folded blank 30. Mounted on the upper die block 44 is a long nosed narrow-edged block 45 urged downwardly bysprings 46 and guided by pins 47 for limited reciprocation relative to the block 44. The memher 45 descends with the block 44 to bear against the wire 28 and hold the blank in position in the groove of the die 43; r V

Cams 48 fixed to the block 44 force sliding diemembers 49 into engagement with the blank so as to further fold the blank around the wire as illustrated. "The springs 46 are compressed" during this part of'the travel of 'block44.

Following the above described forming operations, the trailing edge of the blade is progressively forged, rolled, or otherwise shaped. This may be accomplished'by suitably formed dies 50, 52; 54, '6; 58, 60; and 62,64, as shown in Figs. '4 through 7, inclusive, which illustrate the progressive lengthening and thinning out of the trailing edge of the blade and the gradual'envelopment of the crease of the fold material over the wire so as to embed or enclose the latter substantially'corripletely within the inner crease of the material at the trailing edge of the blade.

Fig. 8 illustrates the step of'imparting the desired'contour to the blade faces and the forward or leading edge of' the blade. This step may be performed by inserting a shoe-like die 66 within the interior'of the partially'completed blade and by forging or otherwise shaping the blade between suitably formed dies 68,70 that surround the" exterior of the blade, substantially as shown. Formation of the blade contour, other than the initial folding of'the trailing edge can be carried on simultaneously with the other steps of the process, the number of steps of whichwill depend upon the choice of materials and the physical size of material and equipment. tions maybe carried out while'the metal is hot or cold depending also upon the material used. 7

'The fin or flash (not shown), formed around the edges 7 of the blade during the shaping operations may then be trimmed, and the ends of the blade trimmed to the desired' length The edges of the curved blade face terminal portions meet or abut along the leading edge of the blade and may be united by welding or brazing, for example. The welded seam may be in one face of the blade rather than at the edge, if desired. After inspection the welds are ground and the blade polished. to obtain the desired edge contour; For more precise dimensioning the blade may be struck in a striking die, if'necessary,

In the vcase of compressor rotor blades or turbine buckets, a foot portion (not shown) may be weldedor otherwise suitably attached to one end of the completed blade for mounting in a complementary mating slot in the periphery'of'a compressor or turbine rotor. Where permissible, the foot may be eliminated and the blade welded or brazed to the rotor or blade. carrying member.

The opera 2,799,919 A 5 p e In a word, the blade can be used many manner and mounted in any fashion, for the invention is concerned in its broader aspect with the'reduction of stresses in the formation of folded sheet metal structures in general.

In an alternative process of manufacture, the body of the blade may be formed from tube stock. For this method, operations in the shaping of the blade body and insertion of the wire reinforcing means in the sharply creased edge or edges thereof would be similar to those already described. Shoe-like dies inserted within the interior of the tube would be employed.

The invention is not limited to the particular blade face contour shown and may be readily applied to the formation of both rotor and stator 'blading elements of other shapes. Where blades'with sharply folded leading and trailing edges are to be formed, as could be employed for turbine buckets, for example, wire reinforcements at both of the folded edges of the bucket may be i used.

Although a preferred embodiment of the process of invention has been described and illustrated, numerous other variations, modifications, and applications within..

the scope thereof will be apparent to those skilled in the art to which it appertains. Particularly, the process of the invention is not limited to the manufacture of turbine buckets and the like, but may be utilized in the manufacture of various articles in which a sharply folded part, especially one which is to be reduced to a sharp edge, is required.

I claim:

A method of forming a hollow sheet metal blade having curved blade faces, a rounded leading edge and a sharp thin reinforced trailing edge, said methodincluding the steps of preparing a flat sheet metal blank from which said blade is to be formed, positioninga length of reinforcing wire of relatively harder material composition than the metal ofsaid blank on said blank substantially parallel to and midway between the ends of said blank, folding saidblank about said wire, forcing opposite portions of'the blank adjacent said wire together to further foldsaid portions around said wire, subjecting said; blank to a series of complementary forging dies to progressively lengthen and thin out the folded portions of said blank'and to gradually envelop said wire within the material ofthe blank at the-folded edge to substantially completely embed said wire therein while retaining the original cross section of said wire, forging the blade face' contours, into said blank; and uniting the edges of said blank along the leading edge of said blank.

References Cited in the file of this patent UNITED STATES PATENTS 

